1. Field of the Invention
The present invention relates generally to fastener devices and methods, and more particularly in certain embodiments to fastener devices used to attach grating sheets to supporting structural members, or to attach structural members to grating sheets, or to attach grating sheets to adjacent grating sheets.
2. Description of the Related Art
Bar-type floor and deck grating is used as a floor in many industrial facilities. Bar-type grating is manufactured in rectangular sheets, typically two to four feet wide and 20 to 30 feet in length. Bar-type grating is normally constructed as open grids having parallel spaced load-supporting bearing bars running the length of the sheet of grating, interconnected by cross-bars running perpendicular thereto. The cross-bars are welded to each bearing bar that they pierce. The principal dimension by which grating is selected is the grating thickness, which determines its load-bearing strength. The grating thickness represents the dimension measured from the contact surface of the structural member on which the grating is installed to the top surface of the grating upon which people walk. While most grating is made in thicknesses of one inch, grating thicknesses may range from less than one inch up to any thickness, although thicknesses above two inches are not commonplace.
Bar-type floor and deck grating is typically made out of metal or fiberglass. The means for attaching the grating to the structural member is affected by the material out of which the grating is fabricated.
One prior art method used to attach sheets of metal grating to structural support members was simply to weld the bearing bar to the supporting structural member. A problem with welding is that each weld damages the paint system already in place on the structure. Welding also may weaken the structural steel, especially heat treated steel. Welding the metal grating is costly because it requires a well-trained person and expensive equipment. Furthermore, welding may not be possible without shutting down the facility due to safety reasons. Also, direct welding of the bearing bars to the structural support member does not permit the grating to be easily removed. The welding method was used in many power generating stations across the U.S. in the past, and many of these installations now suffer safety problems due to loose grating. This loosening was caused by corrosion in the atmosphere, continual expansion and contraction in normal ambient temperature fluctuations, and similar effects. Therefore, problems arise when welding is used to fasten grating to structural support members.
Another method of fastening grating is by the use of saddle clips, also called m-clips and butterfly clips. The saddle clip typically comprises sheet metal pressed to have two downwardly facing channels spaced apart to fit over two adjacent bearing bars of the grating and a connecting portion between these two channels. The connecting portion of the saddle clip includes a hole for receiving a stud bolt or other threaded fastener. The clip is placed over the upper edge of two adjacent bearing bars and an upstanding stud bolt which has been welded to the structural support member. A nut fastens the clip to the stud bolt and secures the grating. The welding of the stud bolt results in many of the same problems associated with welding the bearing bars to the structural support members as discussed above.
Alternatively, a hole may be drilled through the structural support member and a bolt and nut used to fasten the saddle clip to the structural support member. This technique is impractical due to the fact that it requires one person to work from above the grating and a second person to work from below the grating. Additionally, this technique often results in a need for extensive scaffolding being erected below the structural support member. The holes drilled in structural support members weaken the support member and encourage the formation of rust and corrosion unless touch-up painting is performed.
Another technique used to fasten the grating with a saddle clip is with a threaded tap and bolt combination which first drills a hole, then follows by cutting screw threads in the hole, and lastly follows with a threaded bolt portion which tightens in the threaded hole. Once again, each hole encourages the formation of corrosion, and the tap and bolt combination often fails to adequately perform due to breaking before the tapping is finished or stripping the threads in the final tightening process. The broken fasteners are usually left in place and an additional hole is drilled nearby which further weakens the structural member. This technique also requires the use of power tools.
In another technique, saddle clips may be attached to powder-cartridge driven studs which have been fired into the structural steel member by a stud gun powered by a 0.22 caliber blank cartridge. This method is often not allowable due to the stud gun's inherent danger as a weapon.
Referring now to FIG. 1, a mechanical type of grating fastener employing a saddle clip is shown and described in U.S. Pat. No. 4,362,422 to Zinkann et al. This fastener has an upper saddle clip which is connected to a lower assembly by a threaded bolt. The lower assembly includes a base member having an engagement portion which slants downwardly away from the grating bearing bars engaged by the upper saddle clip and which bears against the lower surface of a structural member flange or leg. The lower assembly also includes a swivel clamp which is spring biased to swivel, after passing through the bearing bars, into a position which will engage the underside of the same two bearing bars engaged by the saddle clip. This fastener can be installed by one person working from above without any welding or drilling. As the threaded bolt is tightened, one half of the force in the threaded bolt is transmitted through the engagement portion to the lower surface of the structural member flange and one half is transmitted through the swivel clamp to the grating bearing bars. Thus, only one half of the total force in the bolt is being utilized to secure the grating to the structural member. In addition, the downward slant of the engagement portion generally does not provide a surface for "gripping" the flange of the structural member. Furthermore, certain structural members as classified by the American Institute of Steel Construction (AISC), such as angles and W shapes, have a uniform flange or leg thickness instead of a tapered flange thickness, which is typical for channels and S-shapes. Thus, the slanted engagement portion of the Zinkann fastener does not provide uniform engagement of the flange irrespective of the type of structural member. Additionally, the swivel clamp which engages the underside of the bearing bars has a fixed height which controls the bearing contact of the engagement portion of the base member with the flange. Lastly, when removal of the fastener is attempted, the swivel clamp prevents the fastener from coming up through the grating bars, so the common way to remove the fastener is to remove the bolt and let it fall, creating a safety problem. Since the flange thickness varies from structural member to structural member, the bearing contact of the base member and thus the effectiveness and securing ability of the Zinkann fastener also varies from structural member to structural member.
In addition to the problems discussed above, saddle clips generally do not hold up well in the industrial settings where they are employed. In most of the industrial-type settings where grating is used, heavy objects are transported and routinely placed or dropped on the grating. As a result of heavy objects being placed or dropped on the grating, the M-shaped saddle clips tend to bulge outwardly due to their shape and lack of resistance to bending along the length of the saddle clip between the grating bearing bars. This problem is aggravated by the fact that, during the formation of a saddle clip, the flat piece of metal that is to become the saddle clip must be deformed precisely at the point where the portion of the saddle clip is exposed above the surface of the grating, thus weakening this portion of the metal. The effect of a saddle clip bulging outward is a loosening of the attachment of the saddle clip to the adjacent bearing bars, causing the attachment of the grating to the support member to become loose and ineffective.
Therefore, it would be desirable to have a simple, reliable, inexpensive and versatile mechanical fastener which can securely fasten grating to structural support members without the requirement of any welding or drilling and which can be installed by one person working from above. The fastener should provide a firm and secure attachment of grating to structural support members, regardless of the size and shape of the support member, for extended periods of time in all conditions.